if-conv: Fix -fcompare-debug bugs in ifcvt_local_dce [PR94283]

Hi!

The following testcase shows -fcompare-debug bugs in ifcvt_local_dce,
where the decisions what statements are needed is based also on debug stmt
operands, which is wrong.
So, this patch makes sure to never add debug stmt to the worklist, or never
add an assign to worklist just because it is used in a debug stmt in another
bb.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2020-03-24  Jakub Jelinek  <jakub@redhat.com>

	PR debug/94283
	* tree-if-conv.c (ifcvt_local_dce): For gimple debug stmts, just set
	GF_PLF_2, but don't add them to worklist.  Don't add an assigment to
	worklist or set GF_PLF_2 just because it is used in a debug stmt in
	another bb.  Formatting improvements.

	* gcc.target/i386/pr94283.c: New test.


	Jakub

On Tue, 24 Mar 2020, Jakub Jelinek wrote:

> Hi!
> 
> The following testcase shows -fcompare-debug bugs in ifcvt_local_dce,
> where the decisions what statements are needed is based also on debug stmt
> operands, which is wrong.
> So, this patch makes sure to never add debug stmt to the worklist, or never
> add an assign to worklist just because it is used in a debug stmt in another
> bb.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.

> 2020-03-24  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR debug/94283
> 	* tree-if-conv.c (ifcvt_local_dce): For gimple debug stmts, just set
> 	GF_PLF_2, but don't add them to worklist.  Don't add an assigment to
> 	worklist or set GF_PLF_2 just because it is used in a debug stmt in
> 	another bb.  Formatting improvements.
> 
> 	* gcc.target/i386/pr94283.c: New test.
> 
> --- gcc/tree-if-conv.c.jj	2020-01-12 11:54:38.495381997 +0100
> +++ gcc/tree-if-conv.c	2020-03-23 17:13:13.823724294 +0100
> @@ -2917,9 +2917,12 @@ ifcvt_local_dce (class loop *loop)
>    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
>      {
>        stmt = gsi_stmt (gsi);
> -      if (gimple_store_p (stmt)
> -	  || gimple_assign_load_p (stmt)
> -	  || is_gimple_debug (stmt))
> +      if (is_gimple_debug (stmt))
> +	{
> +	  gimple_set_plf (stmt, GF_PLF_2, true);
> +	  continue;
> +	}
> +      if (gimple_store_p (stmt) || gimple_assign_load_p (stmt))
>  	{
>  	  gimple_set_plf (stmt, GF_PLF_2, true);
>  	  worklist.safe_push (stmt);
> @@ -2940,7 +2943,7 @@ ifcvt_local_dce (class loop *loop)
>  	  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs)
>  	    {
>  	      stmt1 = USE_STMT (use_p);
> -	      if (gimple_bb (stmt1) != bb)
> +	      if (!is_gimple_debug (stmt1) && gimple_bb (stmt1) != bb)
>  		{
>  		  gimple_set_plf (stmt, GF_PLF_2, true);
>  		  worklist.safe_push (stmt);
> @@ -2963,8 +2966,7 @@ ifcvt_local_dce (class loop *loop)
>  	  if (TREE_CODE (use) != SSA_NAME)
>  	    continue;
>  	  stmt1 = SSA_NAME_DEF_STMT (use);
> -	  if (gimple_bb (stmt1) != bb
> -	      || gimple_plf (stmt1, GF_PLF_2))
> +	  if (gimple_bb (stmt1) != bb || gimple_plf (stmt1, GF_PLF_2))
>  	    continue;
>  	  gimple_set_plf (stmt1, GF_PLF_2, true);
>  	  worklist.safe_push (stmt1);
> --- gcc/testsuite/gcc.target/i386/pr94283.c.jj	2020-03-23 17:16:50.324494226 +0100
> +++ gcc/testsuite/gcc.target/i386/pr94283.c	2020-03-23 17:16:42.238614863 +0100
> @@ -0,0 +1,5 @@
> +/* PR debug/94283 */
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -fcompare-debug -mavx2" } */
> +
> +#include "../../gcc.dg/fold-bopcond-1.c"
> 
> 	Jakub
> 
>

Hi.

This patch caused:

gcc /home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c -O3 -g -fno-tree-dce -c
during GIMPLE pass: ifcvt
/home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c: In function ‘broken030599’:
/home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c:2:1: internal compiler error: Segmentation fault
     2 | broken030599(int *n)
       | ^~~~~~~~~~~~
0xe32f1f crash_signal
	../../gcc/toplev.c:328
0x7ffff7999f1f ???
	/usr/src/debug/glibc-2.31-3.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0x104ffe5 verify_use
	../../gcc/tree-ssa.c:884
0x1054607 verify_ssa(bool, bool)
	../../gcc/tree-ssa.c:1161
0xd4fb05 execute_function_todo
	../../gcc/passes.c:1992
0xd507ae execute_todo
	../../gcc/passes.c:2039
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

Martin

On Tue, 24 Mar 2020, Martin Liška wrote:

> Hi.
> 
> This patch caused:
> 
> gcc
> /home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c
> -O3 -g -fno-tree-dce -c
> during GIMPLE pass: ifcvt
> /home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c:
> In function ‘broken030599’:
> /home/marxin/Programming/gcc/gcc/testsuite/gcc.c-torture/compile/990625-2.c:2:1:
> internal compiler error: Segmentation fault
>     2 | broken030599(int *n)
>       | ^~~~~~~~~~~~
> 0xe32f1f crash_signal
> 	../../gcc/toplev.c:328
> 0x7ffff7999f1f ???
> 	/usr/src/debug/glibc-2.31-3.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
> 0x104ffe5 verify_use
> 	../../gcc/tree-ssa.c:884
> 0x1054607 verify_ssa(bool, bool)
> 	../../gcc/tree-ssa.c:1161
> 0xd4fb05 execute_function_todo
> 	../../gcc/passes.c:1992
> 0xd507ae execute_todo
> 	../../gcc/passes.c:2039
> Please submit a full bug report,
> with preprocessed source if appropriate.
> Please include the complete backtrace with any bug report.
> See <https://gcc.gnu.org/bugs/> for instructions.

Likely

  /* Delete dead statements.  */
  gsi = gsi_start_bb (bb);
  while (!gsi_end_p (gsi))
    {

needs to instead work back-to-front for debug stmt adjustment to work